In the processing of semiconductor wafers of silicon or other materials in the manufacture of integrated circuit chips, the wafers are confined in carriers, sometimes called cassettes, oftentimes in batches of 25. The wafers are arranged in a stack-like configuration and each wafer is in a spaced and confronting relation with adjacent wafers to accommodate spraying of liquids and gases onto the wafers and onto the faces of the wafers. The carriers have typically been molded of plastics.
The nature of the plastic material will vary, according to the particular part of the wafer processing in which the carrier is being used. For instance, for a simple storing and cleaning of the wafers, the plastic in the carriers may be polyethylene, or polypropylene or other inexpensive plastics. Many of the carriers are made of plastics which are resistant to the deteriorating effect of strong chemicals such as acids, and resistant to higher temperatures, and those plastics may include various fluorocarbon plastics such as perfluoroalkoxy (known commercially as Teflon PFA, manufactured by E.I. Dupont DeNemours & Co. of Wilmington, Del.) and others. Most of the various plastics are at least somewhat influenced by high temperatures to which they are exposed from time to time and are weakened somewhat by such higher temperatures so that the carriers may not maintain the exact shape to which they are originally formed.
Although the amount of deformation in the carriers is rather minimal in smaller sizes, as for wafers up to five and six inches in diameter, the sizes of wafers are being substantially increased to sizes of ten inches to 16 inches in diameter. Carriers of such size as to hold those large wafers may be subject to an undue deformation due to the influence of higher temperatures.
The usual working range of temperatures for Teflon PFA plastics is up to approximately 180.degree. C. (350.degree. F.) and the nominal melting point of Teflon PFA is approximately 302.degree.-306.degree. C. (575.degree.-590.degree. F.). Prior wafer carriers have been substantially as illustrated in U.S. Pat. Nos. 3,961,877; 4,471,716, and 4,493,418.
Certain carriers made of quartz rods for extremely high temperature use, as in baking ovens, may be somewhat as illustrated in U.S. Pat. No. 4,515,104. One other form of quartz "boat" is illustrated in U.S. Pat. No. 4,389,967.
Plastic carriers have many advantages over quartz carriers in the normal processing of silicon wafers. Plastic carriers are considerably more inexpensive, and are considerably less likely to damage the wafers being carried, among other distinct advantages.